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Departments of 1 Surgery and 2 Pathology, University of Texas Southwestern Medical School and Dallas Veterans Affairs Medical Center, Dallas, Texas 75216
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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The induction of cyclooxygenase is an
important event in the pathophysiology of acute lung injury. The
purpose of this study was to examine the synergistic effects of various
cyclooxygenase products (PGE2, PGI2,
PGF2
) on thromboxane A2
(TxA2)-mediated pulmonary microvascular dysfunction. The
lungs of Sprague-Dawley rats were perfused ex vivo with Krebs-Henseleit
buffer containing indomethacin and PGE2 (5 × 10
8 to 1 × 107 M), PGF2 (7 × 109 to 5 × 106 M), or PGI2 (5 × 108 to 2 × 105 M). The TxA2-receptor
agonist U-46619 (7 × 108 M) was
then added to the perfusate, and then the capillary filtration coefficient (Kf), pulmonary arterial pressure
(Ppa), and total pulmonary vascular resistance (RT) were
determined. The Kf of lungs perfused
with U-46619 was twice that of lungs perfused with buffer alone
(P = 0.05). The presence of PGE2,
PGF2, and PGI2 within the perfusate of lungs
exposed to U-46619 caused 118, 65, and 68% increases in
Kf, respectively, over that of lungs perfused with
U-46619 alone (P < 0.03). The RT of lungs
perfused with PGE2 + U-46619 was ~30% greater than that
of lungs exposed to either U-46619 (P < 0.02) or
PGE2 (P < 0.01) alone. When paired measurements
of RT taken before and then 15 min after the addition of
U-46619 were compared, PGI2 was found to attenuate
U-46619-induced increases in RT (P < 0.01). These
data suggest that PGE2, PGI2, and
PGF2 potentiate the effects of TxA2-receptor
activation on pulmonary microvascular permeability.
capillary filtration coefficient; pulmonary vascular resistance; isolated perfused lung model
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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THROMBOXANE A2 (TxA2)
has been incriminated as an important mediator of the pulmonary
microvascular dysfunction that characterizes tissue ischemia
and reperfusion injury (29), endotoxin exposure (9), and cutaneous
thermal injury (14). In these conditions, as well as others,
TxA2 has been shown to cause vasoconstriction and enhanced
microvascular permeability. Upregulation of cyclooxygenase is an
important event in the generation of TxA2 during acute
inflammatory states. Cyclooxygenase catalyzes the incorporation of
molecular oxygen into arachidonic acid, yielding a cyclic endoperoxide
(PGG2); subsequent peroxidation yields PGH2,
the precursor for the synthesis of TxA2 and
PGE2, PGI2, and PGF2. In
general, each of these cyclooxygenase products is released by the lung
in response to a particular inflammatory stimulus, albeit in varying
amounts (9, 14).
Despite their common origin, the physiological effects of these
substances on the pulmonary microvasculature are diverse. For example,
TxA2 and PGF2 are constrictors of the
pulmonary vasculature in rats, whereas PGI2 is a potent
vasodilator (4, 5). Furthermore, TxA2 profoundly increases
microvascular permeability, whereas the other agents have little, if
any, effect by themselves (20, 27). Several investigators have reported
that PGE2 and PGI2 potentiate the effects of
histamine, bradykinin, and interleukin-1 on microvascular permeability
(2, 34, 35). This observation, as well as the frequency with which
PGE2 and other prostaglandins are released with
TxA2 during acute inflammatory states, led us to postulate
that PGE2, PGI2, and PGF2
potentiate the proinflammatory effects of TxA2 on the
pulmonary microvasculature.
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METHODS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Isolated, Perfused Lung Model
Pathogen-free Sprague-Dawley rats (250-350 g) were anesthetized with pentobarbital sodium (40 mg/kg ip). A median sternotomy was performed, and the pulmonary arterial trunk and left atrium were cannulated via the right and left ventricles, respectively. The heart and lungs were excised en bloc, and the lungs were suspended by a ligature from a force transducer (TSD 125C; Biopac Systems, Santa Barbara, CA) for continuous measurement of lung weight. The lungs were perfused with Krebs-Henseleit buffer containing 3% BSA at 0.04 ml · g body wt1 · min1
and ventilated with room air at a rate of 60 strokes per minute. The
Krebs-Henseleit buffer consists of an aqueous solution containing (in
mM) 128 NaCl, 4.7 KCl, 1.2 MgSO4, 3.2 CaCl2,
1.2 KH2PO4, 25 NaHCO3, and 6.7 dextrose. The perfusate was bubbled with a 95% O2-5%
CO2 mixture to maintain a normal pH (7.40-7.5).
Pulmonary arterial pressure (Ppa) and pulmonary venous pressure (Ppv)
were continuously measured with pressure transducers (TSD 104A; Biopac Systems) with zero reference at the level of the apex of the lung. These measurements were continuously recorded by a Biopac data acquisition unit (MP100 manager version 3.2.3, hardware version 1.1f,
Biopac Systems) interfaced with a personal computer (Dell Computer,
Austin, TX). The perfusate was maintained in a 37°C water bath. The
first 75 ml of perfusate were discarded to remove blood elements from
the vascular space; thereafter, the perfusate was recirculated. The
total volume of the recirculating buffer was 70 ml. In each case, the
lungs were perfused under zone III conditions with arterial pressure > venous pressure > airway pressure. The mean airway pressure was
2-3 mmHg and was maintained below Ppv (3-4 mmHg) by altering
the height of the venous reservoir. The lung preparations were
isogravimetric immediately before all measurements of pulmonary
vascular tone and permeability.
Experimental Protocol
Determination of the effect of indomethacin on U-46619-induced
pulmonary microvascular dysfunction.
An initial set of experiments (Fig.
1A) was performed to determine the
effect of indomethacin on U-46619-induced changes in pulmonary
microvascular function. There were four experimental groups defined by
the composition of the perfusate: 1) Krebs-Henseleit buffer
alone (n = 5), 2) Krebs-Henseleit buffer + U-46619
(n = 7), 3) Krebs-Henseleit buffer + indomethacin
(n = 8), and 4) Krebs-Henseleit buffer + indomethacin + U-46619 (n = 6). In this study, indomethacin (100 µM; Sigma Chemical, St. Louis, MO) was added to the perfusate at
the beginning of the experiment; 15 min later, U-46619 (7.1 × 108 M) was added to the perfusate of the
appropriate experimental groups. After an additional 15 min of ex vivo
perfusion, pulmonary microvascular dysfunction was assessed by
measuring the capillary filtration coefficient
(Kf), total vascular resistance (RT), and pulmonary
vascular pressures as described below.
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,9-epoxymethanoprostaglandin
F2) is a thromboxane-endoperoxide receptor agonist that
has been commonly used to mimic the physiological effects of
TxA2 (4, 22, 23, 25). The concentration of U-46619 was
chosen based on a dose-response curve relating increasing
concentrations of U-46619 to increases in Kf in
this experimental system (data not shown). This concentration of
U-46619 is associated with increases in Kf similar
to those seen with in vivo models of acute lung injury (29). Lastly,
the increases in Kf associated with U-46619 have
been found to be completely inhibited by the thromboxane receptor
antagonist SQ-29548 (2 µM; data not shown).
Determination of the effect of PGE2 and
PGF2 on U-46619-induced pulmonary
microvascular dysfunction.
In these and subsequent experiments (Fig. 1B), indomethacin
(100 µM) was added to the perfusate of the isolated, perfused lung
model to inhibit the generation of endogenous prostanoids (3, 5, 37,
38). This concentration has been previously shown to inhibit the
release of TxA2, PGF2, and PGI2
in an experimental model similar to that employed in these experiments (3, 5). In this particular study, PGE2 (Oxford Biomedical Research, Oxford, MI; 1 × 108 M, 5 × 108 M, 1 × 107 M) or PGF2 (Cayman
Chemical, Ann Arbor, MI; 7 × 109
M, 5 × 107 M, 1 × 106 M, 5 × 106 M) was added to the perfusate at the
beginning of the experiment; 15 min later, baseline measurements of Ppa
and Ppv were obtained. U-46619 (7.1 × 108 M) was then added to the perfusate
and allowed to circulate for 15 min, after which Ppa and Ppv were again
measured and the Kf and vascular resistance were determined.
were prepared in
Krebs-Henseleit buffer according to the supplier's recommendations.
The concentrations and mode of administration of PGE2 and
PGF2 in these experiments were based on the experience
of other investigators utilizing similar experimental models (4, 5, 15,
23, 30, 34). The addition of these substances to the Krebs-Henseleit
buffer had no effect on the pH of the perfusate.
Determination of the effect of PGI2 on U-46619-induced
pulmonary microvascular dysfunction.
In this experiment (Fig. 1C), the ex vivo lung model was
perfused with Krebs-Henseleit buffer containing indomethacin (100 µM)
for 15 min as described above. PGI2 (Oxford Biomedical
Research; 2 × 108 M, 5 × 108 M, 2 × 107 M, 2 × 106 M, 2 × 105 M) was then added to the perfusate,
and afterward baseline measurements of Ppa and Ppv were obtained.
Immediately thereafter, U-46619 (7.1 × 108 M) was added to the perfusate; 7 min
later a second infusion of PGI2 was given as described
above. Seven minutes later (15 min after the addition of U-46619), Ppa
and Ppv were measured, and vascular resistance and
Kf were determined.
Measurement of Pulmonary Microvascular Dysfunction
Kf.
Pulmonary microvascular permeability was quantitated by determining
Kf as has been previously described by our
laboratory (29) and that of other investigators (11, 39). Briefly, 15 min after the addition of U-46619, the capillary pressure prior to
elevating Ppv (Pcpre) was measured using the double
occlusion technique (1, 28). Ppv was then elevated
8-10 mmHg by raising the height of the venous reservoir. This
results in a two-component weight gain consisting of an initial rapid
increase related primarily to recruitment and distension of the
vascular bed (minutes 0-1) and a second slow constant
weight increase due to fluid filtration across the microvasculature
(minutes 1-5). After 5 min of elevated Ppv, Pc was again
measured before returning Ppv to baseline (Pcpost). Kf was calculated as shown in Eq. 1
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(1) |
W is the change in lung weight between minutes 1 and
5 of partial venous outflow occlusion, T is the duration of elevated Ppv during which W is measured, and P is the difference between Pcpost and Pcpre.
Kf is normalized to body weight (expressed as
g · min1 · mmHg1 · 100 g body wt1). This methodology correlates
well with the time 0 extrapolation technique (39).
Pulmonary vascular resistance.
Immediately before the addition of U-46619, Ppa and Ppv were recorded
and compared with measurements obtained 15 min after the addition of
U-46619. RT was calculated as the total pressure drop
across the lung as expressed in Eq. 2
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(2) |
is the flow through the isolated perfused lung. In
the isogravimetric state, the pulmonary circulation can be represented as a simple linear model in which Ppa is separated from Pc by a
precapillary resistance (arterial resistance, Ra) and Pc is separated from Ppv by a postcapillary resistance (venous resistance, Rv) (1). Therefore, where RT is determined in
the isogravimetric state, Ra and Rv can be
calculated as follows
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(3) |
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(4) |
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(5) |
1 · min1 · 100 g body wt1). RT was also
expressed as the absolute difference in determinations of
RT obtained before and 15 min after the addition of U-46619 to the ex vivo lung perfusion. This methodology minimizes variability between lung perfusions in that each lung serves as its own control. Furthermore, this methodology allows determination of the effect of
each PG on U-46619-induced vasomotor activity after quantitation of the
PG's effect on basal vasomotor tone.
In these determinations of Kf and vascular
resistance, Pc was measured with the double occlusion method as
described by Allison et al. (1) and Townsley et al. (28). This
methodology has been demonstrated to correlate closely with
measurements of isogravimetric capillary pressure in both normal and
acutely injured lungs (1, 28).
Statistical Analysis
All data are expressed as means ± SE. The sample sizes of the experimental groups ranged from four to eight. The data were compared by ANOVA with a Student-Newman-Keuls test (SigmaStat; Version 2.0; SPSS; Chicago, IL). Statistical significance was considered for a type 1 error of <5%. All P values represent the results of post hoc comparisons. All experiments were approved by the Committee on the Care and Use of Animals at the University of Texas Southwestern Medical School and Dallas Veterans Affairs Medical Center.| |
RESULTS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Effect of Indomethacin on Pulmonary Microvascular Function
The Kf of lungs exposed to U-46619 in the absence of indomethacin was more than three times greater than that of lungs perfused with Krebs-Henseleit buffer alone (Fig. 2; P < 0.02). The Kf of lungs exposed to U-46619 in the presence of indomethacin (100 µM) was about twice that of lungs perfused with Krebs-Henseleit buffer containing indomethacin but without U-46619 (P = 0.05). The Kf of lungs exposed to U-46619 in the presence of indomethacin was ~40% less than that of lungs perfused with U-46619 without indomethacin (P < 0.03). Lesser concentrations of indomethacin (10 µM) did not have this effect in that the Kf of lungs exposed to U-46619 in the presence of 10 µM indomethacin was 0.023 ± 0.005 g · min1 · mmHg1 · 100 g body wt1; this value was not different
from that of lungs exposed to U-46619 in the absence of indomethacin,
which was 0.019 ± 0.003 g · min1 · mmHg1 · 100 g body wt1. As shown in
Fig. 2, indomethacin (100 µM) did not appear to affect the baseline
permeability of the lungs.
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Indomethacin also appeared to have important effects on U-46619-induced
vasoconstriction. In the absence of indomethacin, U-46619-induced
vasoconstriction was evidenced by a 22% (P = 0.04), 36%
(P < 0.01), and 19% (P = 0.01) increase in Ppa,
RT, and Pc, respectively, when compared with measurements
in lungs perfused with Krebs-Henseleit buffer alone. These data are
shown in Table 1. In the presence of
indomethacin, U-46619 caused a 22% increase in Ppa (P < 0.01) but no significant change in Pc (P = 0.16) or RT (P = 0.1). Furthermore, the RT of
lungs perfused with indomethacin + U-46619 was 25% less than that of
lungs exposed to U-46619 in the absence of indomethacin
(P = 0.01). Indomethacin's effect on U-46619-induced
vasoconstriction appeared to be localized primarily to the precapillary
location, in that the Ra of lungs exposed to indomethacin + U-46619 was ~30% less than that of lungs exposed to U-46619 in the
absence of indomethacin (P = 0.01). Of interest, the
presence of indomethacin (100 µM) within the perfusate did not appear
to affect basal pulmonary vasomotor tone in the absence of U-46619.
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Effects of Prostaglandins on Pulmonary Microvascular Function
Kf.
The presence of PGE2 (5 × 108 M), PGF2 (5 × 106 M), or PGI2 (5 × 108 M) within the perfusate
significantly enhanced the effect of U-46619 on pulmonary microvascular
permeability. These data are shown in Fig.
3. The Kf of lungs
perfused with U-46619 + PGE2, PGF2, or
PGI2 was 118, 65, and 68% greater, respectively, than that
of lungs perfused with U-46619 alone (P < 0.03). Furthermore, the Kf of lungs perfused with U-46619 + PGE2, PGF2, or PGI2 was 4.4, 2.3, and 2.3 times that of lungs perfused with the respective prostaglandins alone (P < 0.01). In the absence of U-46619,
PGE2, PGF2, and PGI2, at the
same concentrations as used above, had no effect on pulmonary
microvascular permeability.
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8 M had no significant effect on
U-46619-induced increases in Kf, whereas 1 × 107 M was associated with an increase in
Kf similar to that of 5 × 108 M. The Kf of
lungs exposed to U-46619 and 1 × 108 M PGE2 was not different
from that of lungs exposed to U-46619 alone (0.009 ± 0.0004 vs. 0.011 ± 0.001 g · min1 · mmHg1 · 100 g body wt1; n = 4 and
7, respectively). In contrast, the Kf of lungs
exposed to U-46619 and either 5 × 108 M PGE2 (0.024 ± 0.004 g · min1 · mmHg1 · 100 g body wt1; n = 6) or 1 × 107 M PGE2
(0.0245 ± 0.004 g · min1 · mmHg1 · 100 g body wt1; n = 4) was
significantly greater than that of lungs perfused with U-46619 alone
(0.011 ± 0.001 g · min1 · mmHg1 · 100 g body wt1; n = 7; P < 0.05) or indomethacin alone (0.006 ± 0.001 g · min1 · mmHg1 · 100 g body wt1; n = 8; P < 0.05). Concentrations of PGF2 <5 µM (7 × 109 to 1 × 106 M) and concentrations of
PGI2 <5 × 108 (2 × 108 M) had no effect on
U-46619-induced changes in Kf, whereas
concentrations >5 × 108 M had an
effect similar to the latter (data not shown).
Pulmonary Vascular Pressures and Resistance
The effect of PGE2 (5 × 108 M), PGF2 (5 × 106 M), and PGI2 (5 × 108 M) on pulmonary vasomotor tone is
shown in Table 2. In the absence of
U-46619, the addition of PGE2, PGF2, or
PGI2 to the perfusate of the ex vivo lung model had no
effect on Ppa or Ppv when compared with those lungs perfused with
buffer alone. Of interest, the RT of lungs perfused with
PGF2 or PGI2 was significantly greater than
that of lungs exposed to Krebs-Henseleit buffer alone (P = 0.01 for both substances). This appeared to be due principally to a 40%
greater Ra in the lungs exposed to these prostaglandins (P = 0.01). The RT of lungs perfused with
PGE2 was not statistically different from that of lungs
perfused with buffer alone (P = 0.057).
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The RT of lungs exposed to PGE2 + U-46619 was
significantly greater than that of lungs exposed to U-46619 alone
(P < 0.02). This increase appeared to be due principally to a
49% increase in Ra over that of lungs exposed to U-46619
alone (P < 0.01). In contrast, PGE2 + U-46619 did
not appear to alter either Ppa or Pc when compared with measurements
taken in lungs exposed to U-46619 alone. The addition of U-46619 to
lungs perfused with PGF2 or PGI2 did not
increase Ppa, Pc, or RT over that associated with the
prostaglandin itself or that caused by U-46619 alone.
Figure 4 illustrates the effect of
PGE2, PGF2, and PGI2 on
U-46619-induced vasoconstriction by comparing the RT of the ex vivo lung model immediately before and 15 min after the addition of
U-46619 to the perfusate. In these paired measurements, U-46619 caused
a significant increase in RT (P < 0.05) compared
with measurements taken immediately before the addition of U-46619.
PGI2 attenuated the increase in RT associated
with U-46619 (P < 0.01), whereas PGE2 and
PGF2 had no significant effect. Expression of the Ppa
data in this manner produced identical results (data not shown).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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The generation of TxA2 by the lung during acute
inflammatory states is often accompanied by the release of
PGE2, PGF2, and PGI2 (9, 14).
Although synergism between PGE2 and PGI2 and
various proinflammatory substances such as histamine, bradykinin, and
interleukin-1 has been well described (2, 34, 35), there have been few
studies examining the effect of these prostaglandins on
TxA2-mediated changes in pulmonary microvascular
permeability. The data presented in this study suggest the following:
1) PGE2, PGF2, and PGI2
do not alter microvascular permeability when administered individually
into an isolated, buffer-perfused rat lung; 2) each of these
prostaglandins potentiates the proinflammatory effects of
TxA2-receptor activation on pulmonary microvascular permeability; 3) indomethacin (100 µM) attenuates U-46619-induced effects on pulmonary microvascular permeability and vascular
resistance; and 4) PGI2 attenuates
TxA2-induced vasoconstriction.
Various investigators (12, 20, 21, 27) have examined the individual
effects of PGE2, PGF2, and PGI2
on pulmonary microvascular permeability in normal animal models,
including the rat. In contradistinction to their very active role in
the regulation of local vasomotor tone, the results of the present study, as well as those of other investigators (20, 21, 27), suggest
that these exogenously administered prostaglandins do not directly
alter pulmonary vascular permeability, at least when administered into
a buffer-perfused lung model in the concentrations utilized in this study.
To the authors' knowledge, there are no studies examining the effect
of PGE2 and PGF2 on
TxA2-mediated changes in pulmonary microvascular
permeability and only two studies examining the effect of
PGI2 (37, 38). In the latter two reports (37, 38), the
investigators, utilizing an ex vivo newborn lamb lung model, found that
the Kf of lungs exposed to PGI2 and a
TxA2-receptor agonist
(9,11-epithio-11,12-methano-TxA2) was significantly greater than that of lungs exposed to either PGI2 or
TxA2-receptor activation alone. This increase in fluid
filtration was accompanied by a reduction in vascular hydrostatic
pressure, suggesting that, in addition to a direct effect on
microvascular permeability, PGI2 may have increased
pulmonary Kf by increasing vascular surface area
(37, 38). These results are similar to those of the present study in
that the Kf of lungs exposed to PGI2
and U-46619 was nearly 70% greater than that of lungs exposed to
U-46619 alone (P < 0.02). Furthermore, this occurred in a
setting in which PGI2 prevented U-46619-induced
vasoconstriction. Of interest in one of the Yoshimura studies (38),
PGI2 alone was found to induce an acute lung injury
manifested by "a diffuse hemorrhagic edema." This is clearly
different from the experience reported in the present study [as
well as that reported by other investigators (12, 21)] in which
PGI2 alone had no effect on Kf. Even in the presence of U-46619, the increase in Kf
associated with PGI2 exposure was much more modest than
that suggested by Yoshimura et al. (38). The reason for this difference
is unclear, although fundamental differences in the experimental models
are likely to be important [e.g., a sanguineous perfusate was
utilized in the Yoshimura study (38), whereas an asanguineous buffer
was used in the present study]. Furthermore, the total amount of
PGI2 administered in the Yoshimura study was more than 100 times greater than that of the present study (about 300 µg over 180 min in the Yoshimura study vs. 2.6 µg in the present study).
It is also possible that neutrophils, sequestered within the ex vivo
lung model during harvesting, may have contributed to the enhanced
microvascular function that characterized exposure of the lungs to
U-46619 + PGE2 or PGF2. The importance of sequestered neutrophils in the microvascular dysfunction of the ex vivo
perfused lung model was initially suggested by Seibert et al. (24) in
1993 in a study in which neutrophils sequestered within the perfused
lung were found to contribute significantly to the enhanced
permeability associated with pulmonary ischemia-reperfusion injury. One may postulate that in the present study perfusion of the
lung with U-46619 [and perhaps PGF2 and
PGI2 (13, 17, 33, 40)] may have acted on sequestered
neutrophils, resulting in the generation of a respiratory burst and,
ultimately, a neutrophil-mediated microvascular dysfunction (18, 26). Other more recent studies have suggested that U-46619, as well as
PGE2, PGF2, and PGI2, inhibits
neutrophil activation, at least as manifested by increases in
intracellular free calcium, leukoaggregation, and the release of
superoxide radical, 
-glucuronidase, and leukotriene B4
(22, 32, 36). These more recent observations would appear to be
inconsistent with the notion that U-46619 or PGE2,
PGF2, or PGI2 increased pulmonary
microvascular permeability by activating on neutrophils sequestered
within the lung.
Other studies have suggested that activation of the endothelial cell
TxA2/PGH2 receptor may directly alter
microvascular permeability by changing the endothelial cytoskeletal
structure, with resultant changes in cell shape and cell-cell
continuity (31). This would suggest a possible second mechanism by
which PGF2 and PGI2 may work through the
TxA2/PGH2 receptor to enhance microvascular permeability (13, 17, 33, 40). Although these studies clearly suggest
that PGF2 and PGI2 may activate the
TxA2/PGH2 receptor, the relative affinity of
TxA2 receptors for PGI2 and PGF2
is extremely low when compared with that of TxA2 for U-46619 (19, 33, 40). Furthermore, most of these studies were performed
using pharmacological doses in in vitro models. Lastly,
PGE2 has been shown to promote bradykinin-induced edema formation (within the skin), although the mechanism by which this occurs (i.e., whether it is related to neutrophil activation via the
EP3 receptor, a direct effect on the microvascular
permeability, or an effect of increased blood flow) remains speculative
(2, 6, 34, 35). Furthermore, to the investigators' knowledge, no one
has examined the effect of circulating PGE2 on pulmonary vasomotor tone or permeability in a model similar to that utilized in
the present study.
In contrast to the paucity of studies examining the effects of
PGE2, PGF2, and PGI2 on
TxA2-mediated changes in pulmonary microvascular
permeability, there have been numerous studies examining the potential
therapeutic effects of prostaglandins, particularly PGE2
and PGI2, on pulmonary microvascular dysfunction (7, 10). Brigham et al. (7) have shown that the administration of
PGE2 limits endotoxin-induced increases in pulmonary
microvascular permeability. In a more recent study, the induction of
PGE2 and PGI2 release by transfecting a
recombinant cyclooxygenase gene into the pulmonary microvasculature was
found to attenuate endotoxin-induced vasoconstriction and pulmonary
edema (8), an effect attributed, at least in part, to PGE2-
and PGI2-mediated inhibition of TxA2 release by
the lung itself or inflammatory cells such as neutrophils or platelets
sequestered within the lung (8). If a similar mechanism had been
operative in the present study, one would have anticipated a reduction,
not increase, in Kf. Furthermore, the concentration
of TxB2 (the stable metabolite of TxA2) was
measured within the perfusate of several of the lungs exposed to
PGE2, PGI2, and PGF2 and was
found to be no different from that of lungs not exposed to these
prostaglandins (data not shown).
The addition of indomethacin to the perfusate of the ex vivo lung model appeared to attenuate, but not prevent, U-46619-induced increases in Kf. Previous investigators have suggested that indomethacin attenuates increases in pulmonary microvascular permeability by inhibiting the release of proinflammatory prostanoids, particularly TxA2, by the lung (16, 39). In the present study, the addition of U-46619 to the perfusate resulted in a small but statistically significant increase in the release of PGE2 and TxA2 by the lung. The presence of 100 µM indomethacin within the perfusate prevented this increase in endogenous PGE2 and TxA2 release (data not shown), suggesting that the "protective" effect of indomethacin resulted from an inhibition of endogenous prostaglandin and/or TxA2 release.
In the present study, the RT of lungs perfused with
PGI2 was 40% greater than that of lungs perfused with
buffer alone (P = 0.007), whereas PGI2 totally
prevented the increase in vasoconstriction associated with U-46619
exposure. These results are consistent with those of Zhao
et al. (40) and Williams et al. (33), who demonstrated that higher
concentrations of PGI2 contract rat pulmonary artery rings
or aortic strips [probably via the
TxA2/PGH2 receptor (33, 40)], whereas
lower concentrations and those given in the presence of
vasoconstrictors [e.g., U-46619 (4) or PGF2 (5)] cause vasodilation [possibly via the
PGI2/PGE1 receptor (33)]. The results of
the present study are consistent with the observations of other
investigators who suggested that PGI2 becomes a more potent
vasodilator as the tone of the blood vessel is increased (5).
Similar to PGI2, the RT of lungs perfused with
PGF2 was significantly greater than that of lungs
perfused with Krebs-Henseleit buffer (P = 0.01), an increase
due principally to vasoconstriction of the precapillary segment. This
observation is nearly identical to that published by Barnard et al. (5)
using a similar experimental model. In contrast to PGI2,
however, PGF2 had no effect on U-46619-induced
vasoconstriction. This is perhaps related to the fact that
PGF2 competes less effectively for the
TxA2/PGH2 receptor than does U-46619 (5, 17,
25).
There is very little information available regarding the effect of PGE2 on pulmonary vasomotor function. In the present study, the RT of lungs perfused with U-46619 + PGE2 was significantly greater than that of either U-46619 (P < 0.02) or PGE2 alone (P < 0.05), suggesting that PGE2 potentiated the vasoconstriction associated with U-46619. Enthusiasm for this conclusion is limited by the observations that 1) the Ppa of lungs exposed to PGE2 + U-46619 was not different from that of lungs exposed to U-46619 alone and 2) the presence of PGE2 within the perfusate of the lungs did not appear to affect U-46619-induced vasoconstriction when assessed as the absolute change in RT and Ppa in paired measurements taken immediately before and 15 min after the addition of U-46619 (as shown in Fig. 5).
In summary, these data are consistent with the hypothesis that
PGE2, PGI2, and PGF2 potentiate
the proinflammatory effects of TxA2-receptor activation on
pulmonary microvascular permeability. Although the increase in
pulmonary Kf due to PGI2 + U-46619 may result, in part, from PGI2-induced increases in vascular
surface area, there is little evidence to support such a mechanism for the increase in Kf due to the combined effects of
U-46619 + PGE2 and PGF2. The synergistic
effects of these prostaglandins on TxA2-induced pulmonary
microvascular dysfunction may contribute to the lung injury that
commonly accompanies systemic inflammatory states.
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ACKNOWLEDGEMENTS |
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This work is supported in part by a Department of Veterans Affairs Merit Review Grant and a Texas Chapter of the American Lung Association Research Grant.
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FOOTNOTES |
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This work was presented in part at the 21st Annual Conference on Shock, June 14-17, 1998, San Antonio, TX.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: R. H. Turnage, Dept. of Surgery, Univ. of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75235.
Received 11 December 1998; accepted in final form 2 November 1999.
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REFERENCES |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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|---|
1.
Allison, RC,
Rippe B,
Prasad VR,
Parker JC,
and
Taylor AE.
Pulmonary vascular permeability and resistance measurements in control and ANTU-injured dog lungs.
Am J Physiol Heart Circ Physiol
256:
H1711-H1718,
1989
2.
Armstrong, RA,
Matthews JS,
Jones RL,
and
Wilson WH.
Characterization of PGE2 receptors mediating increased vascular permeability in inflammation.
Adv Prostaglandin Thromboxane Leukot Res
21:
375-378,
1990.
3.
Barnard, JW,
Barman SA,
Adkins WK,
Longenecker GL,
and
Taylor AE.
Sustained effects of endothelin-1 on rabbit, dog, and rat pulmonary circulations.
Am J Physiol Heart Circ Physiol
261:
H479-H486,
1991
4.
Barnard, JW,
Ward RA,
Adkins WK,
and
Taylor AE.
Characterization of thromboxane and prostacyclin effects on pulmonary circulation.
J Appl Physiol
72:
1845-1853,
1992
5.
Barnard, JW,
Ward RA,
and
Taylor AE.
Evaluation of prostaglandin F2 and prostacyclin interactions in the isolated perfused rat lung.
J Appl Physiol
72:
2469-2474,
1992
6.
Bray, MA,
Cunningham FM,
Ford-Hutchinson AW,
and
Smith MJH
Leukotriene B4: a mediator of vascular permeability.
Br J Pharmac
72:
483-486,
1981[Web of Science][Medline].
7.
Brigham, KL,
Serafin W,
Zadoff A,
Blair I,
Meyrick B,
and
Oates JA.
Prostaglandin E2 attenuation of sheep lung responses to endotoxin.
J Appl Physiol
64:
2568-2574,
1988
8.
Conary, JT,
Parker PE,
Christman BW,
Faulks RD,
King GA,
Meyrick BO,
and
Brigham KL.
Protection of rabbit lungs from endotoxin injury by in vivo hyperexpression of the prostaglandin G/H synthase gene.
J Clin Invest
93:
1834-1840,
1994.
9.
Demling, RH,
Smith M,
Gunther R,
Flynn JT,
and
Gee MH.
Pulmonary injury and prostaglandin production during endotoxemia conscious sheep.
Am J Physiol Heart Circ Physiol
240:
H348-H353,
1981
10.
Demling, RH,
Smith M,
Gunther R,
Gee M,
and
Flynn J.
The effect prostacyclin infusion on endotoxin-induced lung injury.
Surgery
89:
257-263,
1981[Web of Science][Medline].
11.
Drake, R,
Gaar KA,
and
Taylor AE.
Estimation of the filtration coefficient of pulmonary exchange vessels.
Am J Physiol Heart Circ Physiol
234:
H266-H274,
1978
12.
Gunther, R,
Zaiss C,
and
Demling RH.
Pulmonary microvascular response to prostacyclin (PGI2) infusion in unanesthetized sheep.
J Appl Physiol
52:
1338-1342,
1982
13.
Hanasaki, K,
and
Arita H.
A common binding site for primary prostanoids in vascular smooth muscles: a definitive discrimination of the binding for thromboxane A2/prostaglandin H2 receptor agonist from its antagonist.
Biochim Biophys Acta
1013:
28-35,
1989[Medline].
14.
Jin, LI,
LaLonde C,
and
Demling RH.
Lung dysfunction after thermal injury in relation to prostanoid and oxygen radical release.
J Appl Physiol
61:
103-112,
1986
15.
Kaley, G,
Rodenburg JM,
Messina EJ,
and
Wolin MS.
Endothelium-associated vasodilators in rat skeletal muscle microcirculation.
Am J Physiol Heart Circ Physiol
256:
H720-H725,
1989
16.
Ljungman, AG,
Grum CM,
Deeb GM,
Bolling SF,
and
Morganroth ML.
Inhibition of cyclooxygenase metabolite production attenuates ischemia-reperfusion lung injury.
Am Rev Respir Dis
143:
610-617,
1991[Web of Science][Medline].
17.
Mais, DE,
Saussy DL,
Chaikouni A,
Kochel PJ,
Knapp DR,
Hamanaka N,
and
Halushska PV.
Pharmacologic characterization of human and canine thromboxane A2/prostaglandin H2 receptors in platelets and blood vessels: evidence for different receptors.
J Pharmacol Exp Ther
223:
418-424,
1985.
18.
Malik, AB,
Perlman MB,
Cooper JA,
Noonan T,
and
Bizios R.
Pulmonary microvascular effects of arachidonic acid metabolites and their role in lung vascular injury.
Fed Proc
44:
36-42,
1985[Web of Science][Medline].
19.
McMahon, TJ,
Hood JS,
Nossaman BD,
Ibrahim IN,
Feng CJ,
and
Kadowitz PJ.
Influence of SQ30741 on thromboxane receptor-mediated responses in the feline pulmonary vascular bed.
J Appl Physiol
71:
2012-2018,
1991
20.
Misselwitz, B,
and
Brautigam M.
A comparative study of the effects of iloprost and PGE1 on pulmonary arterial pressure and edema formation in the isolated perfused rat lung model.
Prostaglandins
51:
179-190,
1996[Web of Science][Medline].
21.
Ogletree, ML.
Pharmacology of prostaglandins in the pulmonary microcirculation.
Ann NY Acad Sci
384:
191-206,
1982[Web of Science][Medline].
22.
Rotondo, S,
Celardo A,
Evangelista V,
and
Cerletti C.
The endoperoxides/TxA2 analogue, U46619, inhibits human polymorphonuclear leukocyte function.
J Leukoc Biol
57:
72-79,
1995[Abstract].
23.
Santoian, EC,
Angerio AD,
Schneidkraut MJ,
Ramwell PW,
and
Kot PA.
Role of calcium in U 46619 and PGF2a pulmonary vasoconstriction in rat lungs.
Am J Physiol Heart Circ Physiol
257:
H2001-H2005,
1989
24.
Seibert, AF,
Haynes J,
and
Taylor A.
Ischemia-reperfusion injury in the isolated rat lung. Role of flow and endogenous leukocytes.
Am Rev Respir Dis
147:
270-275,
1993[Web of Science][Medline].
25.
Sessa, WC,
and
Nasjletti A.
Dexamethasone selectively attenuates prostanoid-induced vasoconstrictor responses in vitro.
Circ Res
66:
383-388,
1990
26.
Spagnulo, PJ,
Ellner JJ,
Hasid A,
and
Dunn MJ.
Thromboxane A2 mediates augmented polymorphonuclear leukocyte adhesiveness.
J Clin Invest
66:
406-414,
1980.
27.
Stenson, WF,
Chang K,
and
Williamson JR.
Tissue differences in vascular permeability induced by leukotriene B4 and prostaglandin E2 in the rat.
Prostaglandins
32:
5-17,
1986[Web of Science][Medline].
28.
Townsley, MI,
Korthuis RJ,
Rippe B,
Parker JC,
and
Taylor AE.
Validation of double occlusion method for Pc,i in lung and skeletal muscle.
J Appl Physiol
61:
127-132,
1986
29.
Turnage, RH,
LaNoue JL,
Kadesky KM,
Meng Y,
and
Myers SI.
Thromboxane A2 mediates increased pulmonary microvascular permeability after intestinal reperfusion.
J Appl Physiol
82:
592-598,
1997
30.
Wagerle, LC,
and
Busija DW.
Effect of thromboxane A2/endoperoxide antagonist SQ 29548 on the contractile response to acetylcholine in newborn piglet cerebral arteries.
Circ Res
66:
824-831,
1990
31.
Welles, SL,
Shepro D,
and
Hechtman HB.
Eicosanoid modulation of stress fibers in cultured bovine aortic endothelial cells.
Inflammation
9:
439-450,
1985[Web of Science][Medline].
32.
Wheeldon, A,
and
Vardney CJ.
Characterization of the inhibitory prostanoid receptors on human neutrophils.
Br J Pharmacol
108:
1051-1054,
1993[Web of Science][Medline].
33.
Williams, SP,
Dorn GW, III,
and
Rapoport RM.
Prostaglandin I2 mediates contraction and relaxation of vascular smooth muscle.
Am J Physiol Heart Circ Physiol
267:
H796-H803,
1994
34.
Williams, TJ.
Prostaglandin E2, prostaglandin I2 and the vascular changes of inflammation.
Br J Pharmacol
65:
517-524,
1979[Web of Science][Medline].
35.
Williams, TJ,
Jose PJ,
Wedmore CV,
Peck MJ,
and
Forrest MJ.
Mechanisms underlying inflammatory edema: the importance of synergism between prostaglandins, leukotrienes and complement-derived peptides.
Adv Prostaglandin Thromboxane Leukot Res
11:
33-37,
1983[Web of Science][Medline].
36.
Wise, H,
and
Jones RL.
Characterization of prostanoid receptors on rat neutrophils.
Br J Pharmacol
113:
581-587,
1994[Web of Science][Medline].
37.
Yoshimura, K,
Tod ML,
Pier KG,
and
Rubin LJ.
Role of venoconstriction in thromboxane-induced pulmonary hypertension and edema in lambs.
J Appl Physiol
66:
929-935,
1989
38.
Yoshimura, K,
Tod ML,
Pier KG,
and
Rubin LJ.
Effects of a thromboxane A2 analogue and prostacyclin on lung fluid balance in newborn lambs.
Circ Res
65:
1409-1416,
1989
39.
Zanaboni, PB,
Bradley JD,
Baudendistel LJ,
Webster RO,
and
Dahms TE.
Cyclooxygenase inhibition prevents PMA-induced increases in lung vascular permeability.
J Appl Physiol
69:
1494-1501,
1990
40.
Zhao, YJ,
Wang J,
Tod ML,
Rubin LJ,
and
Yuan XJ.
Pulmonary vasoconstrictor effects of prostacyclin in rats: potential role of thromboxane receptors.
J Appl Physiol
81:
2595-2603,
1996
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P < 0.002 vs. lungs perfused with same prostaglandin but in absence of
U-46619.
